Tongue-Eating Parasites with Mayonnaise

by Joseph DeSisto

Tongue-eating parasites that are found in cans of tuna eat tuna, not human, tongues. But that’s a boring headline, so most news outlets left that part out when a woman in Britain found a “thing” in her can of tuna. The victim was one Zoe Butler, who opened her can of Princes tuna chunks this week to find an eyed, globular, undeniably cute invertebrate staring back at her.

Since the specimen was sent back with the tuna can to Princes, Stuart Hine of the Natural History Museum in London had to make do with a photograph in making his identification. He postulated that it might be a parasite related to Cymothoa exigua. Unfortunately, he also mentioned the common name, the tongue-eating louse, to reporters, who got right to work making sure the public knew that we were about to take part in a real-life version of The Bay.

What these reporters didn’t appreciate, sadly, is that the actual life history of Cymothoa is far more interesting and twisted than any sensationalist headline. These creatures belong to the crustacean order Isopoda, and are distantly related to woodlice. Unlike woodlice, however, Cymothoa are roly-poly fish nightmares.

Cymothoa exigua, a tongue-eating isopod. Photo by Marco Vinci.

Cymothoa exigua, a tongue-eating isopod. Photo by Marco Vinci.

As free-living larvae, Cymothoa are all males, and spend their time swimming about in search of a fish host. When several individuals “colonize” a fish, they begin feeding on its gills. If C. exigua is the louse, the host will be red snapper (not tuna). Once a fish has been parasitized, some males will change into females, and mating takes place on the gills or in the fish’s mouth.

The females are the tongue-eaters. Either before or after mating, depending on the species, a female invades the fish’s mouth and begins to suck blood. Extracting blood from the tongue eventually causes the tongue to wither away, after which the female persists on bits of mucus and blood remaining in the fish’s mouth. In C. exigua, this is when mating takes place: a few males will migrate from the host’s gills and mate with the female inside the fish’s mouth.

During all this time, the fish is still able to function, because the female Cymothoa functionally replaces the tongue. So with a new segmented, chitinous, leggy tongue, the fish can still eat and reproduce normally. Eventually, the female’s young emerge as free-living males, and disperse to find a new fish.

So, are tongue-eating parasites dangerous to humans? An adult female can bite in self-defense, and revealing a giant isopod while cleaning a snapper might be emotionally scarring. But rest assured, our tongues are safe. Enjoy your tuna.

For more information:

Driscoll, Brogan. “Mystery ‘Crab’ Found in Tuna Could Actually Be A Tongue-Eating Parasite, Claims Expert.” Huffington Post. 2 Feb 2015. Web. 6 Feb. 2015.

Creighton, Jolene. “Meet The Sex-Changing, Tongue-Eating Parasite.” From Quarks to Quasars. 3 Apr 2014. Web. 6 Feb 2015. <;.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s